Molds for shaping glass and methods for making the same

ABSTRACT

A mold for shaping glass can be made by a method that includes providing a mold body having a shaping surface comprising at least about 90% nickel and modifying the composition of the shaping surface of the mold body by exposing the shaping surface to an oxidizing heat treatment. The oxidizing heat treatment may include a ramping heat treatment, a fixed heat treatment, or both the ramping heat treatment and the fixed heat treatment. The ramping heat treatment may include increasing a heating temperature at a rate from about 20° C./hour to about 500° C./hour to a temperature from about 700° C. to about 1000° C. The fixed heat treatment may include holding the heating temperature from about 700° C. to about 1000° C. for a holding time of at least about 5 minutes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. to Provisional Application Ser. No. 61/754,798, filed on Jan. 21,2013, and is related to “High Purity Nickel Molds for Optical QualityGlass Forming,” U.S. application Ser. No. 14/158,242, contemporaneouslyfiled on Jan. 17, 2014 and also claiming priority under 35 U.S.C. §119of U.S. to Provisional Application Ser. No. 61/754,798, filed on Jan.21, 2013, the content of both of which is relied upon and incorporatedherein by reference in its entirety.

BACKGROUND

1. Field

The present specification generally relates to molds and, morespecifically, to molds for shaping glass.

2. Technical Background

The current demand in modern electronics devices for thin, threedimensional glass substrates that have very high levels of surfacequality has produced a need to find new materials and processes that arecommercially capable of providing defect-free shaped glass substrates.Shaped glass forming generally refers to high temperature processes thatinvolve heating the glass to be formed to a temperature at which it canbe manipulated, and then conforming it to a mold to get the designedshape. Classic methods of shaping glass substrates include televisiontube forming, where a softened glass gob is pressed between male &female molds, and bottle forming, where glass is blown in a pair ofhollowed molds.

In shaping operations, mold material selection is often the key tosuccess. In order to optimize the shape and surface quality of theformed glass article, the mold material must: 1) have excellentoxidation and corrosion resistances at the process temperatures; 2) haveminimal reaction with the glass (no sticking); and 3) be strong enoughat the process temperature in order to resist the deformation anddistortion from the forming force.

In reality, it can be difficult to select one material to meet all theabove requirements. One solution has been to apply coatings on the moldsurface to get the combined merits of the various materials to achieveforming success. Coated molds are the most commonly used in the glassforming industries today. Uncoated molds (or bare molds) are rare, andare limited to lower-end glass products such as bottles and certainglassware that don't require high surface quality. If bare molds areused, there is generally some level of lubrication applied to help withthe forming process and to retain surface quality. These lubricants aredifficult to consistently apply and require a secondary cleaning step toremove. For higher-end products, especially for optical-quality productssuch as press-formed camera lenses, coatings have been deemed asessential.

Although coatings help to meet the challenges in glass forming process,they create new problems. For example, coatings can add significantcosts and new variables to manage the processes. More importantly,coatings often deteriorate during operation and lose functionality,limiting the lifetime of the mold and necessitating frequent re-coating.Therefore, there is an unmet need in the area of high-end, high qualityglass substrates to obtain better mold materials that are commerciallycapable of providing defect-free, shaped glass substrates.

SUMMARY

The embodiments described herein relate to molds for shaping glass andmethods for making the same. According to one embodiment, a mold forshaping glass can be made by a method that may comprise providing a moldbody having a shaping surface comprising at least about 90% nickel andmodifying the composition of the shaping surface of the mold body byexposing the shaping surface to an oxidizing heat treatment. Theoxidizing heat treatment may comprise a ramping heat treatment, a fixedheat treatment, or both the ramping heat treatment and the fixed heattreatment. The ramping heat treatment may comprise increasing a heatingtemperature at a rate from about 20° C./hour to about 500° C./hour to atemperature from about 700° C. to about 1000° C. The fixed heattreatment may comprise holding the heating temperature from about 700°C. to about 1000° C. for a holding time of at least about 5 minutes. Thenickel oxide layer may have an average thickness from about 500 nm toabout 20 micron.

In another embodiment, a mold for shaping glass may comprise a mold bodyhaving a shaping surface and a nickel oxide layer on the shapingsurface. At least a portion of the mold body near the shaping surfacemay comprise at least about 90% nickel. The nickel oxide layer may havean average thickness from about 500 nm to about 20 micron and the nickeloxide layer may have an average surface roughness (R_(a)) of less thanor equal to about 1 micron on the shaping surface of the mold.

In yet another embodiment, a glass article may be made by a methodcomprising supplying a mold for shaping glass and forming a glassarticle by contacting glass with the mold at a temperature sufficient toallow for shaping of the glass. The mold may comprise a mold body havinga shaping surface and a nickel oxide layer on the shaping surface. Atleast a portion of the mold body near the shaping surface may compriseat least about 90% nickel. The nickel oxide layer may have an averagethickness from about 500 nm to about 20 micron, and the nickel oxidelayer may have an average surface roughness (R_(a)) of less than orequal to about 1 micron on the shaping surface of the mold.

Additional features and advantages of the embodiments described hereinwill be set forth in the detailed description which follows, and in partwill be readily apparent to those skilled in the art from thatdescription or recognized by practicing the embodiments describedherein, including the detailed description which follows, the claims, aswell as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts the structure of a mold for shaping glass,according to one or more embodiments shown and described herein;

FIG. 2 graphically depicts the average thickness of nickel oxide layersformed by varied fixed temperatures and holding times; and

FIG. 3 graphically depicts the peak surface roughness of nickel oxidelayers formed by varied fixed temperatures and holding times.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of molds forshaping glass and methods for making molds for shaping glass, examplesof which are illustrated in the accompanying drawings. Wheneverpossible, the same reference numerals will be used throughout thedrawings to refer to the same or like parts. Embodiments of methods formaking molds for shaping glass, as well as embodiments of molds forshaping glass, will be described in more detail herein with specificreference to the appended drawings.

The following description is provided as an enabling teaching. To thisend, those skilled in the relevant art will recognize and appreciatethat many changes can be made to the various embodiments describedherein, while still obtaining the beneficial results. It will also beapparent that some of the desired benefits can be obtained by selectingsome of the features without utilizing other features. Accordingly,those who work in the art will recognize that many modifications andadaptations to the present embodiments are possible and can even bedesirable in certain circumstances and are a part of the presentdescription. Thus, the following description is provided as illustrativeand should not be construed as limiting.

Disclosed are materials, compounds, compositions, and components thatcan be used for, can be used in conjunction with, can be used inpreparation for, or are embodiments of the disclosed method andcompositions. These and other materials are disclosed herein, and it isunderstood that when combinations, subsets, interactions, groups, etc.of these materials are disclosed that while specific reference of eachvarious individual and collective combinations and permutation of thesecompounds may not be explicitly disclosed, each is specificallycontemplated and described herein. Thus, if a class of substituents A,B, and C are disclosed as well as a class of substituents D, E, and F,and an example of a combination embodiment, A-D is disclosed, then eachis individually and collectively contemplated. Thus, in this example,each of the combinations A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C—F arespecifically contemplated and should be considered disclosed fromdisclosure of A, B, and C; D, E, and F; and the example combination A-D.Likewise, any subset or combination of these is also specificallycontemplated and disclosed. Thus, for example, the sub-group of A-E,B-F, and C-E are specifically contemplated and should be considereddisclosed from disclosure of A, B, and C; D, E, and F; and the examplecombination A-D. This concept applies to all aspects of this disclosureincluding, but not limited to any components of the compositions andsteps in methods of making and using the disclosed compositions. Thus,if there are a variety of additional steps that can be performed it isunderstood that each of these additional steps can be performed with anyspecific embodiment or combination of embodiments of the disclosedmethods, and that each such combination is specifically contemplated andshould be considered disclosed.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the meaningsdetailed herein.

The term “about” references all terms in the range unless otherwisestated. For example, about 1, 2, or 3 is equivalent to about 1, about 2,or about 3, and further comprises from about 1-3, from about 1-2, andfrom about 2-3. Specific and preferred values disclosed forcompositions, components, ingredients, additives, and like aspects, andranges thereof, are for illustration only; they do not exclude otherdefined values or other values within defined ranges. The compositionsand methods of the disclosure include those having any value or anycombination of the values, specific values, more specific values, andpreferred values described herein.

The indefinite article “a” or “an” and its corresponding definitearticle “the” as used herein means at least one, or one or more, unlessspecified otherwise

As used herein, the term “substrate” describes a glass sheet that may beformed into a three-dimensional structure.

Generally, a mold for shaping glass can be made by a process thatcomprises providing a mold body having a shaping surface and modifyingthe composition of the shaping surface by forming a nickel oxide layeron the shaping surface. The modification of the composition of theshaping surface may be by exposure of the shaping surface to anoxidizing heat treatment. The oxidizing heat treatment may generallycomprise a ramping heat treatment, a fixed heat treatment, or both,where the ramping heat treatment may comprise increasing the heatingtemperature at a given temperature rate and the a fixed heat treatmentmay comprise holding the heating temperature at a given temperature fora specified holding time. In some embodiments, the oxidizing heattreatment may not comprise the ramping heat treatment, and in some otherembodiments, the oxidizing heat treatment may not comprise the fixedheat treatment. The heating may generally be performed in air, or anyother oxygen containing environment.

Embodiments herein comprise nickel metal-based molds that are useful inthe formation of glass substrates, such as three-dimensional glasssubstrates. The glass substrates may be useful as front and/or backcovers for electronics devices, such as telephones, electronic tablets,televisions etc. In these electronics applications, the shape and thesurface quality of the glass substrate may need to be within very tighttolerances in order to provide not only aesthetic appeal, but also tominimize weaknesses in glass surface, potential electronics issues, andminimize costs.

Referring to FIG. 1, one embodiment of a mold 100 comprising a nickeloxide layer 110 for glass-shaping is depicted. In one embodiment, a mold100 may comprise a mold body 120 that may include a shaping surface 122disposed on the mold body 120. The nickel oxide layer 110 may bepositioned on at least a portion of the shaping surface 122 of the moldbody 120. In the embodiment shown in FIG. 1, the geometry of the shapingsurface 122 defines a cavity in the mold body 120. However, in otherembodiments, the geometry of the shaping surface 122 may define othershapes such as protruded areas of the mold body 120 that may makecontact with the glass being formed. It should be understood that a widevariety geometries of the mold body 120 may be used to form varyingthree dimensional glass articles. In some embodiments, more than onemold body 120 may be utilized to form a glass article. For example, twomold bodies 120 may make contact with opposite sides of a glass body toshape the glass body. Accordingly, in a two-mold embodiment, each moldbody 120 may comprise a shaping surface 122 which makes contact with theglass and is coated with a nickel oxide layer 110, respectively.

The mold 100, prior to the oxidizing heat treatment, may comprise ashaping surface 122 comprising greater than about 90% nickel. The mold100 may be made of a bulk material of greater than about 90% nickel, ormay comprise a layer of at least about 90% nickel on another bulkmaterial. The mold 100 may have high purities of nickel, such ascommercially-pure nickel, for formation of three-dimensional glasssubstrates. High purity and ultra-high purity nickel metals, asdescribed below, may have excellent high temperature oxidation andcorrosion resistances, as well as excellent non-sticking characteristicswhen contacted by the softened glass. High purity and ultra-high puritynickels may be relatively soft, and therefore have been thought to notbe strong enough for conventional glass forming operations. However,because the embodied processes do not apply heavy force on the mold 100,they allow for use of these materials in novel ways.

In one embodiment, the shaping surface 122 may comprise high puritynickel. The high purity nickel mold 100 makes it possible to formoptical-quality glass articles. As used herein, a high purity nickelmolds comprise molds 100 with a composition comprising at least 90%,93%, 95%, 97%, 98%, 99%, 99.5%, 99.9%, 99.95%, or 99.99% nickel. In someembodiments, the shaping surface 122 may comprise about 95% to about99.99% nickel, about 97% to about 99.99% nickel, about 98% to about99.99% nickel, about 99% to about 99.99% nickel, about 99.5% to about99.99% nickel, about 99.9% to about 99.99% nickel, about 95% to about99.95% nickel, about 97% to about 99.95% nickel, about 98% to about99.95% nickel, about 99% to about 99.95% nickel, about 99.5% to about99.95% nickel, about 99.9% to about 99.95% nickel, about 99.9% to about99.95% nickel, about 95% to about 99.9% nickel, about 97% to about 99.9%nickel, about 98% to about 99.9% nickel, about 99% to about 99.9%nickel, about 99.5% to about 99.9% nickel, about 95% to about 99.5%nickel, about 97% to about 99.5% nickel, about 98% to about 99.5%nickel, about 99% to about 99.5% nickel, about 95% to about 99% nickel,about 97% to about 99% nickel, about 98% to about 99% nickel, about 95%to about 98% nickel, about 97% to about 98% nickel, or about 95% toabout 97% nickel.

In some embodiments, the shaping surface 122 may comprise ultra highpurity nickel. As used herein, ultra high purity nickel comprises atleast 99%, 99.5%, 99.9%, 99.95%, or 99.99% nickel. In some embodiments,ultra high purity nickel comprises from about 99% to about 99.99%nickel, about 99.5% to about 99.99% nickel, about 99.9% to about 99.99%nickel, about 99% to about 99.95% nickel, about 99.5% to about 99.95%nickel, about 99.9% to about 99.95% nickel, about 99.9% to about 99.95%nickel, about 99% to about 99.9% nickel, about 99.5% to about 99.9%nickel, or about 99% to about 99.5% nickel.

Examples of nickel compositions that may be used herein include, but arenot limited to, commercially pure nickel grades 200 (99.6% Ni, 0.04% C),201 (99.6% Ni, 0.02% C maximum), 205 (99.6% Ni, 0.04% C, 0.04% Mg), 212(97.0% Ni), 222 (99.0% Ni), 233 (99% Ni), and 270 (99.97% Ni) (See.e.g., Special-Purpose Nickel Alloys, in ASM SPECIALTY HANDBOOK: NICKEL,COBALT AND THEIR ALLOYS, #06178G (ASM International 2000), hereinincorporated by reference in its entirety).

The composition of the shaping surface 122 of the mold 100 may bemodified by exposing the shaping surface 122 to an oxidizing heattreatment. The oxidizing heat treatment may comprises exposing the mold100 to elevated temperatures sufficient to convert at least a portion ofthe nickel at the shaping surface 122 of the mold 100 into nickel oxide.The nickel oxide may comprise a layer over substantially the entireshaping surface 122 of the mold 100.

The oxidizing heat treatment may comprise a ramping heat treatment, afixed heat treatment, or both. For example, the oxidizing heat treatmentmay comprise ramping the heating temperature to a given temperature andthen holding at approximately that temperature. A ramping heat treatmentmay comprise increasing the heating temperature at a given temperaturerate to a target temperature. As used herein, a heating temperature isthe temperature to which the mold 100 is exposed during the oxidizingheat treatment. The rate need not be completely steady (linear functionheating curve), but may be substantially completely steady, or within anestablished range of heating rates. A fixed heat treatment may compriseholding the heating temperature at a given temperature for a specifiedholding time. The specified temperature of the fixed heat treatment neednot be completely constant over the entire course of the holding time,but should be within about 25° C. of the specified fixed temperature.For example, if a fixed heat treatment comprises holding the temperatureat about 800° C., the actual temperature over time may vary betweenabout 775° C. and about 825° C.

In some embodiments, a ramping heat treatment may comprise increasing aheating temperature at a rate of about 20° C./hour, about 30° C./hour,about 40° C./hour, about 50° C./hour, about 60° C./hour, about 70°C./hour, about 80° C./hour, about 90° C./hour, about 100° C./hour, 110°C./hour, about 120° C./hour, about 130° C./hour, 140° C./hour, about150° C./hour, about 200° C./hour, about 300° C./hour, about 400°C./hour, or about 500° C./hour to a target temperature. For example, aramping heat treatment may comprise increasing the heating temperatureat a rate of from about 20° C./hour to about 500° C./hour, from about30° C./hour to about 300° C./hour, from about 40° C./hour to about 200°C./hour, from about 50° C./hour to about 150° C./hour, from about 60°C./hour to about 140° C./hour, from about 70° C./hour to about 130°C./hour, from about 80° C./hour to about 120° C./hour, or from about 90°C./hour to about 110° C./hour. The target temperature may be from about700° C. to about 1000° C., such as from about 800° C. to about 1000° C.,from about 900° C. to about 1000° C., from about 700° C. to about 900°C., from about 800° C. to about 900° C., or from about 700° C. to about800° C.

In some embodiments, the fixed heat treatment may comprise holding theheating temperature to at least about 300° C., 400° C., 500° C., 600°C., 700° C., 800° C., 900° C., or 1000° C. for a holding time. In someembodiments, the fixed heat treatment may comprise holding the heatingtemperature at a temperature of at least about from about 300° C. toabout 1000° C., from about 400° C. to about 1000° C., from about 500° C.to about 1000° C., from about 600° C. to about 1000° C., from about 700°C. to about 1000° C., from about 800° C. to about 1000° C., from about900° C. to about 1000° C., from about 300° C. to about 900° C., fromabout 400° C. to about 900° C., from about 500° C. to about 900° C.,from about 600° C. to about 900° C., from about 700° C. to about 900°C., from about 800° C. to about 900° C., from about 300° C. to about800° C., from about 400° C. to about 800° C., from about 500° C. toabout 800° C., from about 600° C. to about 800° C., from about 700° C.to about 800° C., from about 300° C. to about 700° C., from about 400°C. to about 700° C., from about 500° C. to about 700° C., from about600° C. to about 700° C., from about 300° C. to about 600° C., fromabout 400° C. to about 600° C., from about 500° C. to about 600° C.,from about 300° C. to about 500° C., from about 400° C. to about 500°C., or from about 300° C. to about 400° C. The holding time may be atleast about 5 minutes. For example, the holding time may be from about15 minutes to about 1 week For example, the holding time may be at leastabout 15 min, 30 min, 45 min, 1 hour, 1.5 hours, 2 hours, 3 hours, 4hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours,12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 18 hours, 20 hours, 22hours, or 24 hours. In some embodiments, the holding time may be fromabout 15 minutes to about 4 hours, from about 30 minutes to about 1.5hours, from about 8 hours to about 24 hours, from about 12 hours toabout 20 hours, from about 14 hours to about 18, or from about 15 hoursto about 17 hours.

Following the ramping heat treatment or fixed heat treatment, whicheveris later, the mold's surrounding temperature may be returned to at ornear ambient conditions (about room temperature). The ramping heattreatment may begin at or near ambient conditions.

In some embodiment, the oxidizing heat treatment comprises both aramping heat treatment and a fixed heat treatment. For example, theramping heat treatment may comprise increasing the heating temperatureat a rate from about 50° C./hour to about 150° C./hour to a temperaturefrom about 700° C. to about 900° C., and the fixed heat treatment maycomprise holding the heating temperature from about 700° C. to about900° C. for a holding time from about 14 hours to about 18 hours. Inother embodiments, the ramping heat treatment may comprise increasingthe heating temperature at a rate from about 70° C./hour to about 130°C./hour, from about 80° C./hour to about 120° C./hour, from about 90°C./hour to about 110° C./hour, or about 100° C./hour to a temperaturefrom about 750° C. to about 850° C., from about 750° C. to about 825°C., from about 790° C. to about 810° C., or about 800° C. and the fixedheat treatment may comprise holding the heating temperature from about750° C. to about 850° C., from about 750° C. to about 825° C., fromabout 790° C. to about 810° C., or about 800° C. for a holding time fromabout 10 hours to about 22 hours, 14 hours to about 18 hours, 15 hoursto about 17 hours, or about 16 hours.

In another embodiment, the ramping heat treatment may compriseincreasing the heating temperature at a rate from about 50° C./hour toabout 150° C./hour to a temperature from about 800° C. to about 1000°C., and the fixed heat treatment may comprise holding the heatingtemperature from about 800° C. to about 1000° C. for a holding time fromabout 30 minutes to about 1.5 hours. For example, the ramping heattreatment may comprise the ramping heat treatment may compriseincreasing the heating temperature at a rate from about 70° C./hour toabout 130° C./hour, from about 80° C./hour to about 120° C./hour, fromabout 90° C./hour to about 110° C./hour, or about 100° C./hour to atemperature from about 850° C. to about 950° C., from about 875° C. toabout 925° C., from about 890° C. to about 910° C., or about 900° C.,and the fixed heat treatment may comprise holding the heatingtemperature from about 850° C. to about 950° C., from about 875° C. toabout 925° C., from about 890° C. to about 910° C., or about 900° C. fora holding time from about 5 minutes to 4 hours, from about 15 minutes toabout 2 hours, from about 30 minutes to about 1.5 hours, from about 45minutes to about 1.25 hours, or about 1 hour.

In another embodiment, the oxidizing heat treatment may comprise only aramping heat treatment without a substantial fixed heat treatment, or afixed heat treatment of less than about 15 minutes. For example, theramping heat treatment may comprise increasing the heating temperatureat a rate from about 50° C./hour to about 150° C./hour to a temperaturefrom about 950° C. to about 1000° C., and the fixed heat treatmentcomprises holding the heating temperature from about 950° C. to about1000° C. for a holding time from 0 seconds to about 30 minutes. In otherembodiments, the ramping heat treatment may comprise increasing theheating temperature at a rate from about 70° C./hour to about 130°C./hour, from about 80° C./hour to about 120° C./hour, from about 90°C./hour to about 110° C./hour, or about 100° C./hour to a temperaturefrom about 900° C. to about 1050° C., from about 950° C. to about 1000°C., from about 950° C. to at about 970° C., or about 960° C. and thefixed heat treatment comprises holding the heating temperature fromabout 900° C. to about 1050° C., from about 950° C. to about 1000° C.,from about 950° C. to about 970° C., or at about 960° C. for a holdingtime from 0 seconds to about 30 minutes, such as less than about 1 hour,less than about 45 minutes, less than about 30 minutes, less than about15 minutes, less than about 10 minutes, or less than about 5 minutes.

In another embodiment, the oxidizing heat treatment may comprise a fixedheat treatment at the maximum temperature of a ramping heat treatmentfor less than about 1 hour, less than about 45 minutes, less than about30 minutes, less than about 15 minutes, less than about 10 minutes, orless than about 5 minutes.

The nickel oxide layer 110 on the mold 100 may have an average thicknessof from about 500 nm to about 20 micron, about 1 micron to about 14micron, about 1 micron to about 10 micron, or about 1.5 micron to about2.5 micron. In some embodiments, the nickel oxide layer 110 on the mold100 may have an average thickness of about 100 nm, about 200 nm, about300 nm, about 400 nm, about 500 nm, about 750 nm, about 1 micron, about2 micron, about 3 micron, about 4 micron, about 5 micron, about 6micron, about 7 micron, about 8 micron, about 9 micron, about 10 micron,about 12 micron, about 15 micron, about 18 micron, or about 20 micron.

The glass articles formed using the molds 100 with nickel oxide layers110 described herein may have a reduced number of defects. Ideally, theas formed quality of the part would be as good as the glass sheet fromwhich it is formed. For the most economical process, one desires thatthis surface quality is achieved without further rework or polishing ofthe as formed surface. Defects, as used herein, include, but are notlimited to, dimples (depressions in the glass surface), surfacechecks/cracks, blisters, chips, cords, dice, observable crystals, laps,seeds, stones, orange peel defects (pits in the formed glass from raisedareas on the mold surface, for example 0.1 micron in height with adiameter greater than 30 micron), and stria. In some embodiments, thereare less than an average of 50, 40, 30, 20, 10, 5, 4, 3, 2, or 1 defectsthat are observable by the unaided human eye at 1000 lux in a 25 mm×25mm area on any of the surfaces. In some embodiments, there are less thanan average of 50, 40, 30, 20, 10, 5, 4, 3, 2, or 1 defects that are 150micron in the largest dimension in a 25 mm×25 mm area on any of thesurfaces, as measured by optical microscopy. In some embodiments, thedefect is 1, 2, 3, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 125, or150 micron in the largest dimension.

In another embodiment, glass articles formed using the molds 100 withnickel oxide layers 110 described herein may be essentially flawless. By“essentially flawless,” it is meant that there are no indentations (ordimples) larger than 150 micron in diameter, as measured by an opticalmicroscopy technique, in the surfaces. In some embodiments, there areless than an average of 50, 40, 30, 20, 10, 5, 4, 3, 2, or 1indentations (or dimples) larger than 150 micron in diameter in thelargest dimension in an 25 mm×25 mm area on any of the surfaces, asmeasured by optical microscopy. In some embodiments, the dimple size islarger than 1, 2, 3, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 125, or150 micron in the largest dimension.

Without intending to be held to a particular theory, it is believed thedecrease in the level of defects on the as formed glass surface withhigh purity and ultra-high purity nickel molds 100 is due to at leasttwo causes. First, nickel and nickel oxide appear to be unreactive withthe glass. In particular, aluminosilicate glasses appear to be highlyunreactive. By unreactive it is intended to mean that the glass doesn'treadily stick to the Ni mold material and there is no significantchemical reaction between the glass or glass volatiles that causes thebuild-up of material on the mold surface.

The second reason for the decreased level of defects on the as formedglass surface with high purity and ultra-high purity nickel is thereduced level of impurities and inclusions in the nickel. Theseimpurities comprise one or more of the following: Cu, Fe, Mn, C, Si, S,Mg, Al and Ti. These impurities are typically present in the Ni basedalloys as oxides, sulfides and carbides. In many if not most cases theoxides, sulfides and carbides exist in the microstructure of the Nialloy as a distinct phase, commonly called an inclusion, that israndomly distributed throughout the alloy. A certain percentage of theseinclusions will end up on the machined and polished surface of the mold.During the glass forming process, these inclusions that are at or nearthe mold surface can be reactive with the glass and stick to it, oroxidize and react at a rate that is different from the bulk metal andthus form a protrusion on the mold surface.

Both conditions cause a localized area on the mold surface that canstick to the glass or cause high pressure points that drag across theglass surface during the forming process and cause defects in the asformed surface. It follows that as the high purity and ultra-high puritynickel mold becomes purer, the number of inclusions in the metaldecreases and the frequency of inclusions that intersect the machinedmold surface decreases. Decreased inclusions on the shaping surface 122lead to decreased occurrence of defects on the as formed glass surface.

In some embodiments, the nickel oxide layer 110 may have an averagesurface roughness (R_(a)) of less than or equal to about 1 micron on theshaping surface 122 of the mold 100. In some embodiments, this averagesurface roughness (R_(a)) is determined over an evaluation length, suchas 100 μm, 10 mm, 100 mm, etc. or may be determined based on an analysisof the entire shaping surface. As used herein, R_(a) is defined as thearithmetic average of the differences between the local surface heightsand the average surface height and can be described by the followingequation:

${R_{a} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}{y_{i}}}}},$

-   -   where y_(i) is the local surface height relative to the average        surface height. In other embodiments R_(a) may be less than or        equal to about 0.75 micron, 0.5 micron, or even 0.25 micron over        an evaluation length of 10 mm.

In some embodiments, the nickel oxide layer 110 may have a peak surfaceroughness (R_(p)) of less than or equal to about 1.5 micron on theshaping surface 122 of the mold 100. In some embodiments, this averagesurface roughness (R_(p)) is determined over an evaluation length, suchas 100 μm, 10 mm, 100 mm, 1 cm, etc. As used herein, R_(p) is defined asthe difference between the maximum height and the average height. andcan be described by the following equation:

${R_{p} = {\max\limits_{i}y_{i}}},$where y_(i) is the maximum height relative to the average surfaceheight. In other embodiments R_(p) may be less than or equal to about1.25 micron, 1 micron, 0.75 micron, 0.5 micron, or even 0.25 micron overan evaluation length of 10 mm.

Embodiments of the molds 100 described herein may be used in any formingprocesses, such as 3D glass forming processes. The molds 100 areespecially useful in forming 3D glass articles when used in combinationwith the methods and devices described in U.S. application Ser. Nos.13/480,172 and 13/709,594, herein incorporated by reference in theirentireties. Processes embodied in U.S. application Ser. Nos. 13/480,172and 13/709,594 use a mold temperature fairly close to that of theglass—meaning the mold 100 operates at a temperature in the range of 600to 700° C. The issue of glass sticking to the mold 100 during theforming process is a well-known to increase with increased mold/metaltemperature. These mold temperatures are at least 100-200° C. hotterthan the typical temperature of a mold 100 used in a pressing processand the operational range in which we vacuum form is in a region wheremold to glass sticking occurs and which leads to cosmetic and structuraldefect formation in the glass. The embodied high and ultra-high puritynickel molds provide a novel means of addressing this sticking oradhesion issue and provide glass articles with little to no surfacedefects or flaws.

The molds 100 described herein may be utilized in making glass articlesby forming a glass article by contacting glass with the mold 100 at atemperature sufficient to allow for shaping of the glass. In someembodiments, the nickel molds 100 may be used in the following process:a typical thermal reforming process involves heating the 2D glass sheetto a forming temperature, e.g., a temperature in a temperature rangecorresponding to a glass viscosity of 10⁷ Poise to 10¹¹ Poise or betweenan annealing point and softening point of the glass, while the 2D glasssheet is on top of a mold 100. The heated 2D glass sheet may startsagging once heated. Typically, vacuum is then applied in between theglass sheet and mold 100 to conform the glass sheet to the shapingsurface 122 and thereby form the glass into a 3D glass article. Afterforming the 3D glass article, the 3D glass article is cooled to atemperature below the strain point of the glass, which would allowhandling of the 3D glass article.

The glass articles formed via the embodiments herein may be described byU.S. Prov. Appl. No. 61/653,476. The three-dimensional (3D) glassarticles can be used to cover an electronic device having a display, forexample as part or all of the front, back, and or sides of the device.The 3D cover glass can protect the display while allowing viewing of andinteraction with the display. If used as the front cover, the glassarticles can have a front cover glass section for covering the frontside of the electronic device, where the display is located, and one ormore side cover glass sections for wrapping around the peripheral sideof the electronic device. The front cover glass section can be madecontiguous with the side cover glass section(s).

The preformed glass used to in the processes described herein typicallystarts as a two dimensional (2D) glass sheet. The 2D glass sheet may bemade by a fusion or float process. In some embodiments, the 2D glasssheet is extracted from a pristine sheet of glass formed by a fusionprocess. The pristine nature of the glass may be preserved up until theglass is subjected to a strengthening process, such as an ion-exchangechemical strengthening process. Processes for forming 2D glass sheetsare known in the art and high quality 2D glass sheets are described in,for example, U.S. Pat. Nos. 5,342,426, 6,502,423, 6,758,064, 7,409,839,7,685,840, 7,770,414, and 8,210,001.

In one embodiment, the glass is made from an alkali aluminosilicateglass composition. An exemplary alkali aluminosilicate glass compositioncomprises from about 60 mol % to about 70 mol % SiO₂; from about 6 mol %to about 14 mol % Al₂O₃; from 0 mol % to about 15 mol % B₂O₃; from 0 mol% to about 15 mol % Li₂O; from 0 mol % to about 20 mol % Na₂O; from 0mol % to about 10 mol % K₂O; from 0 mol % to about 8 mol % MgO; from 0mol % to about 10 mol % CaO; from 0 mol % to about 5 mol % ZrO₂; from 0mol % to about 1 mol % SnO₂; from 0 mol % to about 1 mol % CeO₂; lessthan about 50 ppm As₂O₃; and less than about 50 ppm Sb₂O₃; wherein 12mol %≦Li₂O+Na₂O+K₂₀≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %. This alkalialuminosilicate glass is described in U.S. Pat. No. 8,158,543.

Another exemplary alkali-aluminosilicate glass composition comprises atleast about 50 mol % SiO₂ and at least about 11 mol % Na₂O, and thecompressive stress is at least about 900 MPa. In some embodiments, theglass further comprises Al₂O₃ and at least one of B₂O₃, K₂O, MgO andZnO, wherein−340+27.1.Al₂O₃−28.7−B₂O₃+15.6.Na₂O−61.4.K₂O+8.1.(MgO+ZnO)≧0 mol %. Inparticular embodiments, the glass comprises: from about 7 mol % to about26 mol % Al₂O₃; from 0 mol % to about 9 mol % B₂O₃; from about 11 mol %to about 25 mol % Na₂O; from 0 mol % to about 2.5 mol % K₂O; from 0 mol% to about 8.5 mol % MgO; and from 0 mol % to about 1.5 mol % CaO. Theglass is described in U.S. Provisional Patent Ion Application No.61/503,734 by Matthew J. Dejneka et al., entitled “Ion ExchangeableGlass with High Compressive Stress,” filed Jul. 1, 2011, the contents ofwhich are incorporated herein by reference in their entirety.

Other types of glass compositions besides those mentioned above andbesides alkali-aluminosilicate glass composition may be used for the 3Dcover glass. For example, alkali-aluminoborosilicate glass compositionsmay be used for the 3D cover glass. Preferably, the glass compositionsused are ion-exchangeable glass compositions, which are generally glasscompositions containing small alkali or alkaline-earth metals ions thatcan be exchanged for large alkali or alkaline-earth metal ions.Additional examples of ion-exchangeable glass compositions may be foundin U.S. Pat. Nos. 7,666,511, 4,483,700, and 5,674,790 and U.S. patentapplication Ser. No. 12/277,573 (Dejneka et al.; 25 Nov. 2008), Ser. No.12/392,577 (Gomez et al.; 25 Feb. 2009), Ser. No. 12/856,840 (Dejneka etal.; 10 Aug. 2010), Ser. No. 12/858,490 (Barefoot et al.; 18 Aug. 18,2010), and Ser. No. 13/305,271 (Bookbinder et al.; 28 Nov. 2010).

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

It should now be understood that the molds disclosed herein may offerthe advantage of reduced flaws on the surface of glass which is shapedby the herein disclosed molds. It should now also be understood thatmolds with superior surface characteristics may be produced by themethods described herein, particularly by utilizing the heating regimesdisclosed herein to produce oxide layers on the shaping surfaces of themolds.

It is noted that the terms “substantially” and “about” may be utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. These terms are also utilized herein to represent thedegree by which a quantitative representation may vary from a statedreference without resulting in a change in the basic function of thesubject matter at issue.

Various modifications and variations can be made to the embodimentsdescribed herein without departing from the scope of the claimed subjectmatter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

EXAMPLE

Molds were prepared by exposing preformed high purity nickel molds tooxidizing heat treatments of ramping the heating temperature from roomtemperature at 100° C./hr to a fixed heating temperature and holding fora given time period. FIG. 2 shows average thickness of the nickel oxidelayers formed and FIG. 3 shows the peak surface roughness based onholding times and temperatures for the fixed heat treatment. The nickelmold contained at least 99% nickel, sometimes referred to as “201nickel”. The heating was performed in air.

We claim:
 1. A method of making a mold for shaping glass comprising:providing a mold body having a shaping surface comprising at least about90% nickel; and modifying the composition of the shaping surface byforming a nickel oxide layer on the shaping surface by exposing theshaping surface to an oxidizing heat treatment comprising: a rampingheat treatment comprising increasing a heating temperature at a ratefrom about 20° C./hour to about 500° C./hour to a temperature from about700° C. to about 1000° C.; a fixed heat treatment comprising holding theheating temperature from about 700° C. to about 1000° C. for a holdingtime of at least about 5 minutes; or both the ramping heat treatment andthe fixed heat treatment; wherein the nickel oxide layer has an averagethickness from about 500 nm to about 20 micron.
 2. The method of claim1, wherein the oxidizing heat treatment comprises both the ramping heattreatment and the fixed heat treatment.
 3. The method of claim 2,wherein: the ramping heat treatment comprises increasing the heatingtemperature at a rate from about 50° C./hour to about 150° C./hour to atemperature from about 700° C. to about 900° C.; and the fixed heattreatment comprises holding the heating temperature from about 700° C.to about 900° C. for a holding time from about 14 hours to about 18hours.
 4. The method of claim 2, wherein: the ramping heat treatmentcomprises increasing the heating temperature at a rate from about 90°C./hour to about 110° C./hour to a temperature from about 775° C. toabout 825° C.; and the fixed heat treatment comprises holding theheating temperature from about 775° C. to about 825° C. for a holdingtime from about 14 hours to about 18 hours.
 5. The method of claim 2,wherein: the ramping heat treatment comprises increasing the heatingtemperature at a rate from about 50° C./hour to about 150° C./hour to atemperature from about 800° C. to about 1000° C.; and the fixed heattreatment comprises holding the heating temperature from about 800° C.to about 1000° C. for a holding time from about 30 minutes to about 1.5hours.
 6. The method of claim 2, wherein: the ramping heat treatmentcomprises increasing the heating temperature at a rate from about 90°C./hour to about 110° C./hour to a temperature from about 875° C. toabout 925° C.; and the fixed heat treatment comprises holding theheating temperature from about 875° C. to about 925° C. for a holdingtime from about 30 minutes to about 1.5 hours.
 7. The method of claim 1,wherein: the ramping heat treatment comprises increasing the heatingtemperature at a rate from about 50° C./hour to about 150° C./hour to atemperature from about 950° C. to about 1000° C.; and the fixed heattreatment comprises holding the heating temperature from about 950° C.to about 1000° C. for a holding time from 0 seconds to about 30 minutes.8. The method of claim 1, wherein the nickel oxide layer has an averagethickness from about 1 micron to about 14 micron.
 9. The method of claim1, wherein the nickel oxide layer has an average thickness from about 1micron to about 30 micron.
 10. The method of claim 1, wherein the nickeloxide layer has an average thickness from about 2 micron to about 20micron.
 11. The method of claim 1, wherein the nickel oxide layer has anaverage surface roughness (R_(a)) of less than or equal to about 1micron over an evaluation length of 10 mm on the shaping surface of themold.
 12. The method of claim 1, wherein the nickel oxide layer has apeak surface roughness (R_(p)) of less than or equal to about 1.5 micronover an evaluation length of 10 mm on the shaping surface of the mold.13. The method of claim 1, wherein the mold body has a shaping surfacecomprising greater than about 95% nickel prior to modifying thecomposition of the shaping surface.
 14. The method of claim 1, whereinthe mold body has a shaping surface comprising greater than about 99%nickel prior to modifying the composition of the shaping surface.